The discovery of several superfamilies of genomically-encoded, functional noncoding RNAs (ncRNAs) such as microRNAs (miRNAs or miRs) and long noncoding RNAs (lncRNAs) in the control of various cellular processes has expanded our knowledge of “genes” in the cells. It also provides insights into developing novel therapeutic strategies. For instance, the tumor suppressive ncRNAs (e.g., miR-34a) that are depleted in carcinoma tissues may be reintroduced into cancer cells to manage tumor progression (He, et al. (2007) Nature, 447, 1130-1134; Welch, et al., (2007) Oncogene, 26, 5017-5022; and Liu, et al. (2011) Nature Medicine, 17, 211-215). Indeed, a liposome formulated miR-34a, namely “MRX34”, has entered Phase I clinical trial for the treatment of unresectable primary liver cancer or those with liver metastasis from other cancers (Kelnar, et al., (2014) Anal Chem. 86(3):1534-42; and Ling, et al. (2013) Nature Reviews. Drug Discovery, 12, 847-865). However, the lack of efficient method for producing large quantities of inexpensive, naturally-occurring and biologically-functional ncRNA agents hinders the basic research on ncRNA structures and functions as well as the translational research on ncRNA-based therapies. Currently, miRNA agents such as the mimics, precursors and antagomirs are mainly produced via chemical synthesis (Kelnar, et al., (2014) Anal Chem. 86(3):1534-42; Ling, et al., (2013) Nature Reviews. Drug Discovery, 12, 847-865; Takahashi, et al., (2013) Nucleic Acids Research, 41, 10659-10667; and Gebert, et al. (2014) Nucleic Acids Research, 42, 609-621). Although organic synthesis of oligonucleotides may be automated, a projected test or therapeutic dose of 22-nt small RNA agents is astonishingly costly. It is also unclear to what extent chemical modifications would alter RNA structure, biological activity and safety profile despite that the mimics show some favorable pharmacokinetic properties such as a longer half-life. Furthermore, it is extremely difficult to accomplish some naturally-occurring modifications (Cantara, et al. (2011) Nucleic Acids Research, 39, D195-201; Limbach, et al., (1994) Nucleic Acids Research, 22, 2183-2196; Liu, et al., (2013) PloS One, 8, e81922; and Dominissini, et al. (2012) Nature, 485, 201-206) via chemical synthesis, which may be crucial for the biodegradation, function and safety of natural RNAs. In vitro transcription (Beckert, et al., (2011) Methods in Molecular Biology, 703, 29-41) is another way to produce RNA agents in variable lengths. However, in vitro transcription generally generates RNA molecules in a test tube on microgram scale, and the production of larger quantities of RNAs requires more but inexpensive RNA polymerases. Recently, tRNA (Ponchon, et al., (2007) Nature Methods, 4, 571-576; Ponchon, et al., (2009) Nature Protocols, 4, 947-959; Nelissen, et al., (2012) Nucleic Acids Research, 40, e102) and rRNA (Liu, et al., (2010) BMC Biotechnology, 10, 85) have been successfully employed as scaffolds for the production of RNAs, given the fact that tRNAs and rRNAs are present as stable RNA molecules in the cells. The recombinant RNA chimeras are thus isolated, and the target RNAs may be released in demand for structural and biophysical analyses. This recombinant RNA technology provides a novel way for cost-effective and fast production of large quantities of recombinant RNAs (e.g., multimilligrams of RNA species from 1 L bacterial culture). Nevertheless, it has not been shown whether recombinant RNAs comprise any natural modifications (e.g., methylation of a base and pseudouridylation), and whether they are biologically functional in human cells.